The Anchoring effect for two types of vertically foliated slate with different layer thicknesses

Deep-buried steep thin-layered surrounding rock tunnels often face problems of cracking along the layers. Applying bolt supports is a relatively effective method of crack suppression. However, the anchoring effect of steep dip layered rocks, especially at different layer thicknesses, remains unclear. Therefore, the progressive fracture mechanism of two types of slate with different layer thicknesses under non-anchoring, end-anchoring, and full-length anchoring modes was studied through uniaxial cyclic loading and unloading tests, supplemented by monitoring methods such as acoustic emission and digital image correlation. The results show that the peak strength and elastic modulus of the two types of slate specimens with bolts are larger than those without bolts, especially the thick-layered slate specimens increase greatly; the crack development process of thick-layered slate is abrupt, while that of thin-layered slate is dispersed; after anchoring, the energy storage characteristics of thick slate can be significantly strengthened and the final failure modes of the two types of slate are more complete. In the field support, for thin slate, the end-anchoring method can be preferentially selected to utilize fully the overall rate of elongation of the bolt. For thick slate, full-length anchoring can be applied to play the prestress bonding role of bolts and anchoring agent, and suppress interlayer cracking. The results can be used to enrich understanding of the anchoring mechanism of layered surrounding rock, and guide the bolt support design of steep layered surrounding rock in deep tunnelling operations.